Angle limiting reflector and optical dispersive device including the same

Abstract

The invention relates to angle-limiting optical reflectors and optical dispersive devices such as optical spectrum analyzers using the same. The reflector has two reflective surfaces arranged in a two-dimensional corner reflector configuration for reflecting incident light back with a shift, and includes two prisms having a gap therebetween that is tilted to reflect unwanted light and transmit wanted light. A two-pass optical spectrum analyzer utilizes the reflector to block unwanted multi-pass modes that may otherwise exist and degrade the wavelength selectivity of the device.

1 . An optical dispersive device, comprising:
 an optical grating to receive an input light beam along an input direction and to output at least a portion of the input light beam as an output light beam in an output direction; and   a reflector optically coupled with the optical grating, wherein light in the input light beam of a first wavelength diffracted from the optical grating at a first diffraction angle is reflected by the reflector back towards the optical grating and is diffracted in an output direction to form the output light beam;   wherein the reflector comprises:
 first and second prisms of an optically transmissive material positioned with a gap therebetween in an optical path of the light diffracted from the optical grating, 
 wherein at least the first prism is wedged-shaped and comprises a light output surface slanted with respect to a light input surface at a first vertex angle 
 wherein the second prism comprises a light input surface opposite the light output surface of the first prism and not parallel to the light output surface of the first prism, and 
 wherein the gap is formed between the light output surface of the first prism and the light input surface of the second prism. 
   
     
     
         2 . The optical dispersive device of  claim 1 , wherein the light output surface of the first prism is slanted at a second angle with respect to a dispersion plane of the optical grating, and the first vertex angle and the second angle of the first prism are selected so that the total internal reflection at the light output surface of the first prism prevents light of any wavelength in an operating wavelength range of the reflector from contributing into the output light beam after travelling more than twice between the optical grating and the reflector. 
     
     
         3 . The optical dispersive device of  claim 1 , wherein the light output surface of the first prism is slanted at a second angle with respect to a dispersion plane of the optical grating, and the first vertex angle and the second angle are selected so that the total internal reflection at the light output surface of the first prism prevents light of a wavelength at an edge of the operating wavelength range from contributing into the output light beam after travelling more than twice between the optical grating and the reflector. 
     
     
         4 . The optical dispersive device of  claim 1 , wherein light that is diffracted from the optical grating at a second diffraction angle experiences a total internal refraction at the light output surface of the first prism, and is thereby deflecting away from the optical path, and wherein the second diffraction angle corresponds to a ray of a second wavelength from the input light beam, which in the absence of the total internal reflection would have contributed into the output light beam after experiencing more than two passes between the reflecting grating and the reflector. 
     
     
         5 . The optical dispersive device of  claim 1 , wherein light propagating through the gap experiences a first angular chromatic dispersion. 
     
     
         6 . The optical dispersive device of  claim 5 , wherein the light diffracted from the grating impinges upon at least one of the light input surface of the first prism and the light output surface of the second prism at a non-zero angle of incidence that is selected for imparting upon said light a second angular chromatic dispersion, which is opposite in sign to the first angular chromatic dispersion, to at least partially compensate for the first angular chromatic dispersion. 
     
     
         7 . The optical dispersive device of  claim 6 , wherein a third surface of the second prism is tilted with respect to the light input surface of the second prism at an angle that is selected for providing the non-zero angle of incidence at an output surface of the second prism. 
     
     
         8 . The optical dispersive device of  claim 7 , wherein the reflector comprises a mirror disposed in the optical path after the second prism and is to reflect the light diffracted by the optical grating and transmitted through the first and second prisms back towards the optical grating. 
     
     
         9 . The optical dispersive device of  claim 5 , wherein the second prism comprises third and fourth surfaces serving as reflecting surfaces, and wherein the third surface is to reflect the light received from the first prism towards the fourth surface, and the fourth surface is to reflect the light towards an output surface of the second prism to transmit the light towards the optical grating. 
     
     
         10 . An angle limiting reflector for use in a multi-pass optical dispersive device, comprising:
 first and second prisms of a light-transmissive material, disposed one after another in an optical path of an input light beam to receive the input light beam at an input surface of the first prism at a first angle of incidence and to outut the input light beam through an output surface of the second prism,   wherein the first and the second prisms are disposed with a gap between an output surface of the first prism and an input surface of the second prism, and the output surface of the first prism is slanted with respect to the input surface thereof at a first angle that is selected to transmit rays of the input light beam within a range of angles of incidence and to deflect away rays of the input light beam outside the range of angles of incidence, and   wherein the input surface of the second prism is opposite the output surface of the first prism and is not parallel to the output surface of the first prism, and the gap is formed between the light output surface of the first prism and the light input surface of the second prism.   
     
     
         11 . The angle limiting reflector of  claim 10 , wherein rays of the input light beam propagating through the gap acquire a first angular chromatic dispersion after propagating through the gap, and
 the second prism has a first reflecting surface that is oriented to direct the rays of the input light beam propagating through the gap towards the output surface of the second prism, and   wherein orientation of at least one of: the input surface of the first prism, the output surface of the second prism, and the first reflecting surface of the second prism with respect to an optical axis of the rays of the input light beam propagating through the gap is selected for imparting a second angular chromatic dispersion that is opposite to the first angular chromatic dispersion.   
     
     
         12 . The angle limiting reflector of  claim 10 , wherein the input light beam received at the input surface of the first prism is diffracted from an optical grating and rays of the input light beam outside the range of angles of incidence and travelling more than two passes between the reflecting grating and the input surface of the first prism experience a total internal refraction at the light output surface of the first prism. 
     
     
         13 . An optical device, comprising:
 an optical grating to receive an input light beam along an input direction and to output at least a portion of the input light beam as an output light beam in an output direction; and   a reflector optically coupled with the optical grating, wherein light in the input light beam of a first wavelength diffracted from the optical grating at a first diffraction angle is reflected by the reflector back towards the optical grating and is diffracted in an output direction to form the output light beam;   wherein the reflector comprises:
 first and second prisms of an optically transmissive material positioned with a gap therebetween in an optical path of the light diffracted from the optical grating, wherein the first prism comprises a light output surface slanted with respect to a light input surface at a first vertex angle, and the second prism comprises a light input surface opposite the light output surface of the first prism and not parallel to the light output surface of the first prism, and wherein the gap is formed between the light output surface of the first prism and the light input surface of the second prism, 
 wherein rays of the input light beam propagating through the gap acquire a first angular chromatic dispersion after propagating through the gap, and the second prism has a reflecting surface that is oriented to direct the rays of the input light beam propagating through the gap towards an output surface of the second prism, and 
 wherein orientation of at least one of: the light input surface of the first prism, the light output surface of the second prism, and the reflecting surface of the second prism with respect to an optical axis of the rays of the input light beam propagating through the gap is selected for imparting a second angular chromatic dispersion that is opposite to the first angular chromatic dispersion. 
   
     
     
         14 . The optical device of  claim 13 , wherein the light output surface of the first prism is slanted at a second angle with respect to a dispersion plane of the optical grating, and the first vertex angle and the second angle of the first prism are selected so that total internal reflection at the output surface of the first prism prevents light of any wavelength in the operating wavelength range from contributing into the output light beam after travelling more than twice between the reflective optical grating and the reflector. 
     
     
         15 . The optical device of  claim 13 , wherein the light output surface of the first prism is slanted at a second angle with respect to a dispersion plane of the optical grating, and the first vertex angle and the second angle are selected so that total internal reflection at the output surface of the first prism prevents light of a wavelength at an edge of an operating wavelength range of the reflector from contributing into the output light beam after travelling more than twice between the optical grating and the reflector.